Searching the forest for the bees

Timothy B. Wheeler, The Baltimore Sun

— Every week this spring, Pat Groller drove to remote Dorchester Pond and traipsed through the forest, bucket in hand, to check her traps. Her quarry: The mysterious bees that keep wildflowers blooming here year after year.

"It's a trek, but I've enjoyed it," Groller said recently after she'd collected the contents of nine colored plastic cups staked out on the ground. She logs more than 90 miles round-trip from her home in Preston to run traps at three wooded sites on the Eastern Shore.

The 73-year-old grandmother is a volunteer in a small army of citizen scientists taking stock of wild bees in the forests. Organized by the U.S. Geological Survey, the first-of-its kind count is sampling more than 100 wooded sites across Maryland, Delaware, the District of Columbia and Virginia.

"We're interested in what kind of woods the bees are occupying," said Sam Droege, head of the geological survey's bee inventory and monitoring laboratory in Beltsville. The survey is opening a window on a "secret world," as one ecologist put it, of an intricate interaction between forest plants and a dizzying array of pollinating insects.

Scientists are also concerned to find out how wild bees are faring, Droege said, in light of the troubling declines documented in cultivated honey bee populations nationwide.

Researchers reported Thursday that beekeepers nationwide have lost one in three honey bee colonies since last spring, while Maryland's chief apiary inspector said honey bee colony losses among the state's mostly part-time beekeepers approached 50 percent.

A national survey of beekeepers found that they lost one in five honey bee colonies over the winter, fewer than the winter before. But they reported seeing substantial die-off in summer as well, pushing their year-round losses to more than a third.

While many beekeepers and some researchers have linked the die-off to pesticide exposures, the team that did the survey says no single culprit appears responsible for all the honey bee deaths. Those beekeepers who treated their hives for a common but lethal parasite, varroa mite, suffered fewer losses, said Dennis vanEngelsdorp, a University of Maryland entomologist who led the survey.

Domesticated bees are important economically, producing honey and pollinating agricultural crops; wild bees perform a vital role too in maintaining the natural vegetation that we sometimes take for granted.

Scientists have documented declines of wild bumblebees, but Droege said it's not clear that other native bees are in any particular trouble.

"We really don't have an issue that's some kind of mysterious broad-scale decline,'' he said.

Native bees seem unaffected by parasitic mites and other ills plaguing honey bees, which are not native, Droege said.

Droege, 55, and his colleagues have been sampling the wild population for years. They've logged more than 413 species in Maryland, including some honey bees and other non-native bees that were brought here at one time to serve as pollinators and have become "naturalized."

"We're regularly picking up new species of bees," he said, "not because they become new, but because of lack of feet on the ground or eyes in the sky."

The biggest and most familiar of the natives are bumblebees, but many are much smaller, and some downright tiny, such as sweat bees.

Scientists have focused mostly on studying wild bees in meadows and other open areas, but Droege said relatively little is known about the forest denizens.

"We've always known that native bees are in forests," he explained, "and that a lot of them are dependent on some of these forest blooming plants."

Unlike honey bees, which congregate in hives, most of the forest bees are loners that spend the bulk of their lives in the ground. They emerge for just a few weeks in early spring to pollinate flowering plants, shrubs and trees before the forest leafs out and shades the understory from the sun.

Many are "specialists," Droege said, focusing on a particular type of plant or flower.

For example, he said, there's a bee that specializes in collecting nectar and pollen from spring beauty, a ground-hugging pink or white wildflower that's one of the earliest harbingers of spring. One can't exist without the other, he said. In fact, many flowers have features that attract particular pollinators, while discouraging or excluding others.

"Flowers were all designed by bees," Droege said, over millennia of co-evolution.

Dorchester Pond is owned by the Nature Conservancy, one of 13 preserves the conservation group has volunteered as bee sampling sites. Also known as a Delmarva Bay wetland, it contains water only part of the year, and hosts some rare plants and an uncommon type of frog.

The conservancy hopes to learn what bees and other pollinating insects are on its lands, and to use that knowledge in managing the sites to maintain their special natural features, explained ecologist Deborah Landau.

The conservancy has cut loblolly pines around the pond and regularly burns portions of the forest in an attempt to mimic nature and help preserve and restore the rare plants there.

"We know that a lot of these rare plants are returning, but we don't know if they're pollinating, or sustaining,'' Landau said.

By identifying what bees frequent its preserves, the conservancy also may uncover a "secret world," as she put it, of plants served by pollinators that the group's staff also didn't know were there.

"I think there's so much we can learn from plant-insect interactions that we just don't know,'' she said.

Starting in March, volunteers set out nine cups, spaced roughly 10 yards from each other in the collection areas. The cups are of varying colors, to mimic the hues of flowers. The volunteers fill them with propylene glycol, a chemical often used as a preservative in processed foods, and then they go away. Over ensuing days, bees and other pollinators are drawn to the cups and drown in the liquid, which keeps them intact until the weekly collection.

On a recent trap check, Groller filtered assorted bug carcasses and debris from the liquid in each of her cups, then tucked the filter paper and its contents in a plastic bag, marking the pouch with date and location of the sample.

By early May, the mosquitoes and ticks were out in force at Dorchester Pond, but Droege didn't spy any bees in Groller's samples. The flowers they frequent had mostly finished blooming, and the bees likely died off, their wings wrecked by weeks of flying.

The ground has been prepared, though, for next spring, Droege said. The female bees have gathered pollen and nectar in subsurface nests, and laid their eggs there to feed the larvae when they hatch. The young stay below through summer, fall and winter, he explained, waiting for their cue to come out and find new flowers to buzz.

Back at the lab, Droege has set up a bug laundry in the basement. The material in each pouch is painstakingly washed and dried, then placed in a petri dish. Dejen Mengis, a junior biology major at the University of Maryland, College Park, removes each insect, sticks a pin in it, then mounts it in an empty pizza box for Droege to identify.

Stacks of flat boxes fill the lab, each with row upon row of bees. There are so many different species, often with minuscule differences, that Droege often needs to examine specimens under a microscope to be sure.

Droege hopes one day to take the woodland bee survey nationwide. After years of sampling, that study and related ones should give scientists a better handle on how wild bees are doing, what they're doing exactly, and what might be done to keep them doing it.

Meanwhile, Droege shares the storehouse of knowledge he's built up. He emails "bee-of-the-week" profiles to his volunteer network, and gives talks to garden clubs and other groups.

"People don't have much understanding of what the native bees do,'' he said, "and they do all kinds of different and interesting things."